You are asking very technical Qs which I think only a tax specialist can answer! With hindsight you should have done your homework before going shopping! LOL
OK sorry you're probably annoyed at me right now. Anyway, this is my experience but it was a while ago. I was in Australia in 2001 and got tax back at the airport on jewellery. I received cash. Also at the time it was a condition to reclaiming tax, that when you buy the item you tell the seller who had to seal the item in a bag with, I think, a copy of the receipt so you couldn't use the item whilst in the country. Then, I think, at the airport they matched the receipt in the bag with the one the seller gives you (and if they wanted they could inspect the purchase), then I got tax refunded which I then spent at the airport.
May be things have changed since 2001, but if not you've got to tell the seller at the time of purchase you're planning on getting a tax refund so they can package your goods appropriately and give you the right paperwork.
However, like I say, things could have changed since then. Also, I'm not sure if you can claim tax on everything or selected goods.